Surface Review and Letters

Due to the unique properties of titanium (Ti) and its alloys, it has a particularly wide range of applications in aerospace, automotive, medical and other fields. However, the problems of low surface hardness, high friction coefficient and low wear resistance of Ti alloys limit its development to a certain extent. The destruction of Ti and its alloys often occurs on the surface of materials such as wear damage, corrosion, and oxidation resistance. Therefore, the exploration and application of surface strengthening technology is particularly important. The cathodic plasma electrolytic deposition (CPED) technology, as a surface modification technology, can achieve better adhesion and facilitate the material to achieve better comprehensive performance. This paper briefly introduces the basic concepts, principles and development progress of CPED. Starting from the preparation of ceramic coatings, metal coatings, diamond-like carbon films and composite coatings, it summarizes the application of CPED in Ti and its alloys. Applications in alloys to improve thermal oxidation resistance, wear resistance, corrosion resistance, and film-based adhesion. At the end, its development in the new era environment is prospected.

Magnesium alloy with good application potential has a poor corrosion resistance, so it is essential to develop a new corrosion inhibitor and investigate the inhibition mechanism for magnesium alloy. In this work, three vapor phase corrosion inhibitors (VCIs) were used for AZ31B magnesium alloy under a simulated ocean–atmosphere environment, and the inhibition behaviors and mechanisms were studied. The inhibition performances of the three VCIs were evaluated by Digital Still Camera, electrochemical tests and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) combined with X-ray photoelectron spectroscopy (XPS) was used to further explore the inhibition mechanism. Compared to benzoic acid and ammonium benzoate, o-phthalic anhydride can provide the best protection for AZ31B magnesium alloy. The $i$${}_{\text{corr}}$ was reduced from 11.18 $\mu$A cm${}^{-2}$ (blank) to 0.65 $\mu$A cm${}^{-2}$ and the ($R_{\text{f}}$ + $R_{\text{ct}}$) was increased from 1478.1 Ω cm² (blank) to 3129.8 Ω cm² with o-phthalic anhydride as VCI. O-phthalic anhydride combined with Mg${}^{2+}$ to form different complexes with different molecular weights, which developed a more compact protective film on the AZ31B surface. Overall, the o-phthalic anhydride can be utilized as an excellent VCI for AZ31B magnesium alloy in a simulated ocean–atmosphere environment.

As an excellent solid lubrication material, the poor high-temperature tribological properties of diamond-like carbon (DLC) films severely limit their applications. In this study, tungsten (W) was incorporated into Si-doped DLC films fabricated via reactive magnetron sputtering. The effect of the W content ranging from 0 to 13.12 at.% on the film structure, bonding states, mechanical and high-temperature tribological properties of Si and W co-doped DLC (Si–W-DLC) films has been investigated. The results show that a small amount of tungsten incorporation (4.45 at.%, Si–${\text{W}}_{\text{L}}$-DLC) increases the mechanical properties of the Si–${\text{W}}_{\text{L}}$-DLC film without a significant decrease in the fraction of sp³ content. The incorporation of 4.45 at.% W improves the wear resistance and stabilizes the friction coefficient curves at temperatures up to $400^{\circ }$C. The high residual stress caused by the highly distorted C–W bond and the low friction coefficient attributed to the formation of WO₃ on the sliding surface should be responsible for the excellent tribological performance of the Si–${\text{W}}_{\text{L}}$-DLC film. It is believed that the Si and W co-doped DLC film can provide another strategy for expanding the high-temperature application of DLC films.

High speed machining (HSM) is an attractive process for numerous applications due to its potential to increase production rates, reduce lead times, lower costs, and enhance part quality. In this study, high-speed turning operations on AISI D2 steel using a coated carbide cutting tool under dry conditions were conducted. The cutting parameters examined in this investigation were Vc, $f$, and ap, while the outputs measured were surface roughness (Ra), cutting temperature ($T$), and flank wear (VB). To obtain reliable and accurate results, a Taguchi L27 orthogonal array for the 27 experimental runs was employed as well as analysis of variance (ANOVA), response surface methodology (RSM), and artificial neural network (ANN) to develop a constitutive relationship between prediction responses and the cutting parameters. The ANOVA results showed that Vc had a significant effect on $T$ (36.81%) and VB (27.58%), while $f$ had a considerable influence on Ra (24.21%). Additionally, nonlinear prediction models were created for each measured output and their accuracy was evaluated using three statistical indices: coefficient of determination ($R$²), mean absolute percentage error (MAPE), and root mean square error (RMSE). Finally, multi-objective optimization was successfully carried out using the desirability function (DF) approach to propose an optimal set of cutting parameters that simultaneously minimized Ra, $T$, and VB. The optimized cutting parameters were Vc = 477.28 m/min, $f$ = 0.08 rev/min, and ap = 0.8 mm, resulting in Ra = 1.23 $\mu$m, $T$ = $129.9^{\circ }$C, and VB = 0.049 mm.

In this paper, the machinability aspects of Ti-5553 have been experimentally investigated during Electro-Discharge Machining using three different geometrical shapes of copper electrodes i.e. cylindrical, triangular, and square. TIMETAL (Ti-5553) is a titanium-based alloy extensively used for special aerospace and marine applications due to its high strength and higher hardenability. By changing each of the aforementioned process parameters at three distinct levels, experiments based on the ${\text{L}}_{27}$ orthogonal array (OA) design of the experiment (DOE) were carried out. The machining performance has been carried out by utilizing different input parameters i.e. current, pulse off time ($T_{\text{off}}$), flushing pressure ($F_p$), tool shape ($T_s$), and voltage (V) to examine machining performance characteristics like material removal rate (MRR), tool wear rate (TWR), surface roughness (Ra), white layer thickness (WLT), and surface crack density (SCD). Surface integrity in contents of surface morphology and surface topography is discussed herein. In this MRR, TWR, and Ra have been optimized by using a methodology (combining Grey relational analysis method and Taguchi’s philosophy) and found the optimal parameters that will have more MRR and less TWR, Ra. Later SCD and WLT were investigated by employing the optimal setting (A3, B2, C2, D2, E1, F3) and arbitrary setting (A3, B2, C1, D3, E3, F2) and concluded that SCD and WLT are less by utilizing optimal settings for machining as compared to arbitrary settings. Among all three different geometrical shapes of copper electrodes, the cylindrical tool has been found to be the best suitable tool for machine Ti-5553.

The wrought nickel–chromium–cobalt Nimonic 90 alloy is widely used in turbine blades, piston rings and forged tools due to their high stress-rupture strength and creep resistance up to 920^∘C. The application components showed unavoidable wear behaviors at high loads due to the reduced resistance of the components. Hence, in order to increase the wear resistance of this alloy, Inconel 625 and Nimonic 90 particle depositions have been carried out on Nimonic 90 substrate through the laser-cladding techniques to study the microstructure, mechanical and tribological behaviors of alloys. The phases, microstructure and microhardness of the claddings were investigated by X-ray diffractometry (XRD), Transmission electron microscopy (TEM), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS) and hardness test, respectively. Results showed that the mean thickness of the interfacial layer of Inconel 625 and Nimonic 90 was 18.51 ± 4 $\mu$m and 90.68 ± 7 $\mu$m, respectively. The microstructure of the cladding surfaces resulted in dendritic and interdendritic structures. An overall analysis found that the gamma-Ni and hard laves phases were presented in Inconel 625 and Nimonic 90 clad surfaces, respectively. Nimonic 90 clad surface had a high hardness and wear resistance compared with Inconel 625 clad surface and substrate due to the present hard laves phase. Besides, the roughness of the Nimonic 90 clad surface was lower compared with the Inconel 625 clad surface and substrate.

Transition metal substitution can expand the applications of tungsten oxides in chemical sensors, catalysts, and other fields. In order to highlight the effect of TM substitution on the electronic properties of tungsten oxide clusters, the configurations, electronic properties and dipole magnitudes of ${\mathrm{\text{TMW}}}_{n-1}{\mathrm{\text{O}}}_{3n}$ and ${\mathrm{\text{TM}}}_2{\mathrm{\text{W}}}_{n-2}{\mathrm{\text{O}}}_{3n}$ (TM = Ni, Pd and Pt; $n=2-6$) clusters have been investigated via the density functional theory. The structures of ${\mathrm{\text{TMW}}}_{n-1}{\mathrm{\text{O}}}_{3n}$ and ${\mathrm{\text{TM}}}_2{\mathrm{\text{W}}}_{n-2}{\mathrm{\text{O}}}_{3n}$ clusters inherit those of ${\mathrm{\text{W}}}_n{\mathrm{\text{O}}}_{3n}$ ($n$ = 2–6) clusters to some extent except for ${\mathrm{\text{Pd}}}_2{\mathrm{\text{W}}}_2{\mathrm{\text{O}}}_{12}$, ${\mathrm{\text{Pt}}}_2{\mathrm{\text{W}}}_2{\mathrm{\text{O}}}_{12}$, ${\mathrm{\text{Pd}}}_2{\mathrm{\text{W}}}_3{\mathrm{\text{O}}}_{15}$, and ${\mathrm{\text{Pt}}}_2{\mathrm{\text{W}}}_3{\mathrm{\text{O}}}_{15}$ clusters. ${\mathrm{\text{NiW}}}_{n-1}{\mathrm{\text{O}}}_{3n}$ clusters exhibit higher thermodynamic stability than the other ${\mathrm{\text{TMW}}}_{n-1}{\mathrm{\text{O}}}_{3n}$ and ${\mathrm{\text{TM}}}_2{\mathrm{\text{W}}}_{n-2}{\mathrm{\text{O}}}_{3n}$ clusters. ${\mathrm{\text{NiW}}}_2{\mathrm{\text{O}}}_9$, ${\mathrm{\text{NiW}}}_4{\mathrm{\text{O}}}_{15}$, ${\mathrm{\text{Ni}}}_2{\mathrm{\text{O}}}_6$, ${\mathrm{\text{Ni}}}_2{\mathrm{\text{W}}}_4{\mathrm{\text{O}}}_{18}$, ${\mathrm{\text{PdW}}}_3{\mathrm{\text{O}}}_{12}$, ${\mathrm{\text{PdW}}}_5{\mathrm{\text{O}}}_{18}$, ${\mathrm{\text{Pd}}}_2{\mathrm{\text{WO}}}_9$, ${\mathrm{\text{Pd}}}_2{\mathrm{\text{W}}}_4{\mathrm{\text{O}}}_{18}$, ${\mathrm{\text{PtWO}}}_6$, ${\mathrm{\text{PtW}}}_4{\mathrm{\text{O}}}_{15}$, ${\mathrm{\text{Pt}}}_2{\mathrm{\text{O}}}_6$, ${\mathrm{\text{Pt}}}_2{\mathrm{\text{W}}}_4{\mathrm{\text{O}}}_{18}$ clusters display more kinetically stable than adjacent ${\mathrm{\text{TMW}}}_{n-1}{\mathrm{\text{O}}}_{3n}$ and ${\mathrm{\text{TM}}}_2{\mathrm{\text{W}}}_{n-2}{\mathrm{\text{O}}}_{3n}$ clusters. The Mülliken charge transfer amount of ${\mathrm{\text{Pt}}}_2{\mathrm{\text{W}}}_{n-2}{\mathrm{\text{O}}}_{3n}$ clusters is more than that of other ${\mathrm{\text{TMW}}}_{n-1}{\mathrm{\text{O}}}_{3n}$ and ${\mathrm{\text{TM}}}_2{\mathrm{\text{W}}}_{n-2}{\mathrm{\text{O}}}_{3n}$ clusters except for ${\mathrm{\text{Pt}}}_2{\mathrm{\text{W}}}_4{\mathrm{\text{O}}}_{18}$ clusters.

Several researchers have recently expressed interest in additively manufactured electrodes for machining and surface modification applications. The additively manufactured AlSi10Mg tool electrode is one of the promising candidate materials for non-conventional processes. This research investigates the process parameters of laser powder bed fusion (L-PBF) processed AlSi10Mg tool electrodes for the electro-spark deposition process (ESD). The selected deposition parameters, namely, peak current (P_c), pulse-on time (P_on) and deposition time (DT) with various levels and experimentation, are based on the box-behnken design (BBD) of the response surface methodology. The deposition was carried out to analyze the output responses of material deposition rate (MDR), additive tool wear rate (ATWR) and surface roughness (SR). The multi-objective optimization was performed to minimize the ATWR and SR and maximize the MDR. The optimized ESD parameters of P_c = 6 A, P_on = 20$\mu$s, and DT = 5 min were found with predicted responses of MDR = 0.019 mg/min, ATWR = 0.095 mg/min and SR = 3.86 $\mu$m. The deposited surface witnessed the formation of debris, microcracks, and a solidified surface with a dark region and accumulated worn debris that has an elongated and flat shape. The workpiece substrate was exposed to a significant amount of additive tool electrode material (Si, Al, O, Mg, S), and different intermetallic (${\text{Al}}_{26}$ Si) 0.148, Al₂O₃, and Al₂S₃ formations have been recognized. This finding corroborates the efficient usage of L-PBF AlSi10Mg electrodes for ESD processes.

In this study, liquid casting process is used to fabricate AA1050/SiC composites. To increase the wettability of molten Al and improve the adhesion of particles to metallic matrix, liquid casting was selected as the fabrication process. AA1050 and Nano-SiC particles were selected as metallic matrix and reinforcements, respectively. Then, wear, mechanical properties, fracture toughness and forming limit diagram of (FLD) of aluminum composite samples have been investigated experimentally. To do this, AA1050/SiC composite strips with thickness of 1 mm have been fabricated up to eight ARB passes at 300^∘C. The graining was investigated via optical microscopy (OM). The ultimate tensile strength (UTS) of samples improved to 170 MPa registering 168% improvement than the initial monolithic sample. Also, the bonding quality among the layers improved by decreasing the thickness of layers at higher number of passes (increasing the plastic strain). SEM fracture surface morphology of samples after the tensile test showed that by increasing the ARB passes, shear ductile was the fracture mode. So, deep dimples are shrinking slowly relative to the annealed sample. The FLDs’ area dropped sharply for pass 1 and then improved at higher passes as the criterion of formability. Also, wear resistance of composite samples was better than monolithic sample. Moreover, at the 10th pass, the fracture toughness enhanced to the maximum value of 33.5 MPam${}^{1/2}$.